This application claims priorities under 35 U.S.C. Sec.119 to Nos.2001-242508 and 2002-022738 filed in Japan on Aug. 9, 2001 and Jan. 31, 2002, respectively, the entire contents of which are herein incorporated by reference.
1. Field of the Invention
The present invention relates to an opening structure of a fuel tank, more particularly the opening structure of the fuel tank for use in an automotive vehicle. Also, the present invention relates to a method for producing the fuel tank by forming a fuel tank wall with a plurality of plastic layers through blow molding, and forming an opening portion to be integral with the fuel tank wall.
2. Description of the Related Arts
Recently, a fuel tank mounted on an automobile or the like is likely to be made from plastic material. For example, getting popular now is a method for forming a fuel tank by the plastic material through blow molding, and forming an opening portion to be integral with the fuel tank wall. As a result, a plastic fuel tank having an opening portion of a desired structure is getting popular. The structure of the opening portion of the fuel tank as described above is disclosed in Japanese Utility-model Laid-open Publication No.4-7925, for example. In FIG. 3 of that Publication, disclosed is a prior structure, and in FIG. 1, a proposed structure for restraining the height of an opening peripheral wall of the fuel tank. According to the Publication, it is described that engaging portions such as nuts are disposed on a base portion for mounting a cover member thereon, and engaging parts such as bolts are engaged with the engaging portions to secure the cover member to a fuel tank body, or fuel tank wall, so that a sufficient capacity can be obtained in a condition of a limited total height. Also disclosed in Japanese Patent No.2906701 is the structure similar to that disclosed in the above Publication as a prior art.
With respect to the plastic material forming the fuel tank, a plastic member having a plurality of layers is disclosed in Japanese Utility-model Laid-open Publication No.61-83509, for example. In this Publication, disclosed is a blow molded fuel tank with multiple layers, employing multiple plate members with a plurality of component plates adhered together through binding layers.
When the plastic made fuel tank is produced as disclosed in the above Publication No.61-83509, a plastic member having a plurality of layers is employed. This plastic member includes a strength holding member such as high density polyethylene for holding the strength of the fuel tank, a barrier member for protecting the fuel from passing through it, and binding material or the like for binding them. By forming that plastic member through a blow molding method, the fuel tank is produced, together with its opening portion formed simultaneously. When the opening portion is covered by the cover member as disclosed in the aforementioned Publication, the end surface of the opening portion with a plurality of layers may be exposed inside of the fuel tank. In this case, therefore, the fuel might be leaked from the strength holding member of the outermost layer of the plastic member. In the Publication No.4-7925 as described above, it is proposed to connect them by means of a connecting member such as a bolt or the like, with a packing disposed between them. When connecting the cover member with the fuel tank, however, the bolt and the packing of high sealing property will be needed. In this case, even if the packing with a good anti-passing property is employed, there might be caused the leak of fuel through the outermost layer of the plastic member.
Therefore, it is required to form an opening portion to prevent the fuel from passing through the plastic member at an opening portion of the fuel tank, effectively, and also required to connect an annular member engaged with a cover member, with the opening portion integrally.
Accordingly, it is an object of the present invention to provide an opening structure of a fuel tank having a fuel tank wall made of a plurality of plastic layers, to protect the fuel from passing through the plastic member at an opening portion of the fuel tank effectively, and connect an annular member with the opening portion integrally.
It is another object of the present invention to provide a method for forming a fuel tank wall with a plurality of plastic layers through blow molding, and forming an opening portion to be integral with the fuel tank wall, to produce a fuel tank having an opening structure to protect the fuel from passing through the plastic member effectively, and connect an annular member with the opening portion integrally.
In accomplishing the above and other objects, an opening structure of a fuel tank having a fuel tank wall made of plastic layers including at least an outer layer, an inner layer and an intermediate layer, with an opening portion formed to be integral with the fuel tank wall. The opening structure includes a cylindrical portion extended from the fuel tank wall outward thereof to form the opening portion, an overlapping portion extended from an end of the cylindrical portion to enlarge the diameter of the opening portion and bent at a bent portion to form an outer surface parallel with an opening end surface of the opening portion, and a compressed portion with at least a portion of the overlapping portion compressed in a direction perpendicular to the opening end surface of the opening portion. The opening structure further includes an annular member disposed around the opening portion to be in contact with the overlapping portion and the cylindrical portion, and at least a recessed portion for receiving therein a part of the outer layer to be integrally connected with the opening portion. The annular member has a step portion formed inward of the annular member in a radial direction thereof to contact with at least the compressed portion.
Preferably, the recessed portion of the annular member includes a plurality of recesses which are formed to be opened in a direction opposite to a step surface of the step portion. Or, the recessed portion of the annular member may include a plurality of through holes formed on the step portion in the vicinity of the bent portion.
The bent portion may be formed with a lifted wall portion extending parallel with the side surface of the cylindrical portion.
A method for producing a fuel tank by forming a fuel tank wall with plastic layers including at least an outer layer, an inner layer and an intermediate layer, through blow molding, and forming an opening portion to be integral with the fuel tank wall may include a step of forming a cylindrical portion extended from the fuel tank wall outward thereof to form the opening portion, when the fuel tank wall is formed by blow molding, with an annular member placed around the opening portion. The annular member has a step portion formed inward in a radial direction thereof and at least a recessed portion for receiving therein a part of the outer layer to be integrally connected with the opening portion. The method further includes the steps of forming at least a part of the cylindrical portion to be bulged outward thereof in a radial direction thereof, to provide a bulged portion, pressing the bulged portion to form a bent portion bent at the outward of the opening portion in a radial direction thereof, to form an overlapping portion extended from an end of the cylindrical portion to form an outer surface parallel with an opening end surface of the opening portion, and compressing at least a portion of the overlapping portion on the step portion in a direction perpendicular to the opening end surface of the opening portion, to produce a compressed portion.
In the method as described above, the recessed portion of the annular member may include a plurality of recesses formed to be opened in a direction opposite to a step surface of the step portion, or a plurality of through holes formed on the step portion in the vicinity of the bent portion. The annular member may further include at least a leg portion which is integrally formed with the annular member to extend in the direction opposite to the step surface of the step portion, and which may be covered by a part of the outer layer of the opening portion.